Segmented annular sealing ring and method of its manufacture



W. B. MOYER ET AL SEGMENTED Nov. 26, 1968 3,412,977

ANNULAR SEALING RING AND METHOD OF ITS MANUFACTURE Filed April 15, 1965FIG. I.

//vv/v rams WA Y/VE 5. MOVE file/MRO WEE/V7145 @wm THE/R ATTORNEY UnitedStates Patent "ice 3,412 977 SEGMENTED ANNULAR SEALING RING AND METHODOF ITS MANUFACTURE Wayne B. Moyer and Richard W. Gentile, Schenectady,

N.Y., assignors to General Electric Company, a corporation of New YorkFiled Apr. 15, 1965, Ser. No. 448,343 3 Claims. (Cl. 253-39) ABSTRACT OFTHE DISCLOSURE Annular ring of plural segments whose adjoining faces aremade by turning about axes parallel to ring axis.

Background of the invention This invention relates generally tosegmented annular rings and more particularly to a new and improvedsegmented annular turbine shroud and the simplified method of itsmanufacture which the improvement permits.

By way of example, one use for such an annular ring is as a shroud in aturbine. A turbine shroud is a liner member which is supported by theturbine casing or shell and extends radially inwardly into closeproximity to the rotor blades. Its purpose is to prevent leakage of themotive fluid around the blades and in order to allow thermal expansionwithout radial growth, it is often made up of arcuate segments.

Some turbine shrouds which are in present use are machined from castingsin relatively long circumferential segments. The segments are long tominimize leakage at their interfaces and because of their length, theysuffer greater distortion or curling due to a radial temperaturegradient, causing increasing blade tip clearance at some points and rubsat others. The hooks or flanges which hold the long segments to theturbine shell must be short and spaced intermittently. This is toprevent high stresses in the flanges due to circumferential curlingwhich would cause binding in the turbine shell. These intermittentshroud hooks can be easily obtained by using a sand cast segment withraised bosses for hooks. The sand cast segment is slab milled on oneside so as to establish a reference plane. Radial planes are then milledon the ends of the shroud segment. The shroud hooks, I.D., OD. andremaining flat side are subsequently turned in a fixture. Following thisadditional milling is performed on end radial planes to provide radialand axial sealing key grooves. Casting has the attendant disadvantagesof pattern maintenance, loss due to casting flaws, long time cycle, andlower design stress levels consistent with casting quality controlproblems. These extensive milling operations require specialized cuttingtools, with associated high tool maintenance, repetitive handling,setup, and machining time. Together, casting and milling of shroudsegments is an expensive manufacturing method. Reduction of turbine tipclearances is made possible by use of relatively shorter segments whichare advantageous with respect to the distortion and hook stressproblems. However, short shrouds possess the basic disadvantage of highgas bypass leakage through the increased number of interfaces and, madein the manner just described, their cost would be appreciably increased.

Accordingly, it is an object of this invention to provide an improvedsegmented annular ring for use as a shroud for higher efliciency andhigher pressure turbines, and which will provide a high strength flangeto withstand increased temperatures and pressures.

Another object of this invention is to provide an improved segmentedannular ring which will minimize radial and axial leakage through itsinterfaces.

Another object of this invention is to provide an im- CPI 3,412,977Patented Nov. 26, 1968 proved segmented annular ring for use as aturbine shroud which will permit smaller clearances between itself andthe rotor blades by minimizing the effect of shroud curling.

Another object of this invention is to provide an im proved segmentedannular ring with relatively short segments which can be machined frombar stock at reasonable cost without the necessity for using castings orexpensive milling operations.

Another object of this invention is to provide a new method ofmanufacturing segmented annular rings by which the above and otherobjects can be achieved at a minimum cost.

Briefly stated, in accordance with one of its aspects, this inventioncomprises an annular ring of a plurality of segments whose adjoiningfaces, though substantially radial, are arcuate permitting a simplifiedmethod of manufacturing them by turning.

These and other objects, advantages and features of this invention willbe readily appreciated from the following description when considered inconnection with the accompanying drawing, wherein:

FIG. 1 is a fragmentary longitudinal elevation, partly in section, of aturbine shell and one segment of a turbine shroud according to thisinvention.

FIG. 2 is a front elevation of a portion of a turbine shroud accordingto this invention.

FIG. 3 is a radial view looking in the direction of arrows 3-3 of FIG.2, and

FIG. 4 is a plan view showing two of the segments of a segmented annularring on the table of a machine tool.

Description of the invention Referring now to FIG. 1, a segment of aturbine shroud 1 is shown in its environment as it is mounted on aturbine shell 2 within which rotor blades 3 move. The segments are heldto the turbine shell by means of a flange 4 and by fasteners 5 extendingthrough holes 6 in the shell and holes 7 in the segments. Eachindividual segment 1a of shroud 1 as shown in FIGS. 2 and 3 is made withtongues 8 and grooves 9 on both sides for respective mating of adjoiningfaces at interfaces 10. These tongues 8 and grooves 9 provide alabyrinth seal to minimize axial leakage through the shroud 1 at thesegment interfaces. In a preferred embodiment of this invention, tongues8 and grooves 9 are rectangular as shown in FIG. 3. Upon thermalexpansion or contraction, they will continue to provide an effectiveseal since their relationship in the axial direction will be unaffected.Adjacent each segment interface 10, an axial hole 11 extending partlythrough the shroud segment, is made with a diameter at least as great asthe depth of grooves 9.

The axis of each hole 11 lies between tongue 8 and groove 9. A resilienttube 12 with a longitudinal aperture 13 fits into each hole 11. When thesegments are assembled into a complete shroud, tubes 12 prevent radialleakage at interfaces 10 as can be clearly seen in FIG. 2. Thelongitudinal aperture 13 serves two purposes. It facilitates pressingtubes 12 into holes 11 for a tighter fit and therefore a better seal. Italso enables the tubes 12 to give and take during thermal expansions andcontractions in the shroud segments. Another means of preventing radialleakage, which can be used either in conjunction with tubes 12 as shownin FIG. 1, or in the alternative, comprises a strip 14 of a dissimilarmetal, disposed in a dovetail 15 on the inside circumference of theshroud and spanning the interfaces 10 as shown in FIGS. 1 and 3. Thematerial of strip 14 is preferably softer and of a lower meltingtemperature than that of the shroud segments and/or blades as it is alsoused as a. wear member. Location holes 16, as shown in FIGS. 2 and 4,extend partially through the segments on both end faces thereof, for thepurpose of positioning the segments on a jig or fixture for machining.

The method of manufacturing the segments will now be described.Rectangular bar stock workpieces, large enough in section to machinetherefrom one complete shroud segment, are ground to a finish on bothend faces to the desired thickness, which will equal the thickness ofthe turbine shroud. The segments are then positioned in a jig or fixtureand holes 7, 11, and 16 are drilled. The segments are then mounted in acircular array relative to a machine tool such as a vertical turretlathe or vertical boring mill by means of jigs or fixtures and bylocating holes 16.

Convex faces 19 with their tongues and grooves 8 and 9 are then formedby turning relative to a cutting tool such as 21.

The next step is to invert all the segments, positioning them in thesame jigs or fixtures by the opposite set of locating holes 16. Concavefaces 20 with their tongues and grooves 22 and 23 are then formed byturning about another cutting tool, not shown.

The segments are then positioned in a circular array on another fixtureso that tongues and grooves 8, 9, 22, and 23 are mating and locatingholes 16 are mounted on locating pins in the fixture. Concentric faces17 and 18, dovetail 15 and flange 4 are then turned relative to cuttingtools not shown. Since all faces are turned while the segments are flaton fixtures on the machine worktable, the axes of all arcs so turnedwill be parallel.

It should be noted that by the method just described the segments can beturned in lots, an entire shroud annulus being machined at one time.This method of manufacturing shroud segments is clearly simpler and moreeconomical than the casting and milling operations required by previousshroud segments as discussed earlier.

It will be appreciated that the foregoing description discloses asegmented annular ring which has more strength and dimensionalstability, allows less leakage, and is easier and more economicallymanufactured than the prior art structures.

While, for purposes of description, this invention has been related toits use and manufacture as a turbine shroud, it will be obvious to thoseof ordinary skill in the art that the inventive concept embraces alluses of segmented annular members such as packing rings, bearings,turbine nozzle arcs or any such member which prevents leakage and isrequired to expand and contract. Accordingly, it is intended that theinvention be not limited by the environment in which it has beendescribed, but that it encompass all within the purview of the followingclaims.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A turbomachine shroud comprising a segmented annular ring, said ringcomprising a plurality of arcuate segments adjoining one another atinterfaces, the faces of adjoining segments being defined by arcs, theaxes of said arcs being substantially parallel to the axis of said ring,said faces having mating grooved surfaces at the interfaces to allow forrelative movement under changes in temperature, means to fasten adjacentsegments together and obstruct radial flow through said interfaces, andmeans to mount said ring within the easing of a turbomachine.

2. A segmented annular ring as defined in claim 1 said means to fastenadjacent segments and obstruct radial flow comprising axial holesextending partially through said segments at their interfaces, andresilient tubes extending into said holes, the diameter of said holesbeing greater than the depth of the grooves in said surfaces, the axisof each such hole passing through the segments defining the same so thatsaid tubes provide positive fastening of adjacent segments.

3. A segmented annular ring as defined in claim 1, further comprising aplurality of wear strips mounted on said annular ring on the innercircumference thereof and overlapping said segments to obstruct radialflow therebetween.

Refereuces Cited UNITED STATES PATENTS 228,571 6/1880 St. John 277-198749,693 1/1904 Kremer 138-157 X 1,048,657 12/1912 Christensen 277-1571,668,822 5/1928 Schlacks 277-199 1,792,288 2/1931 Dempster 253-392,467,168 4/1949 Traupel 253-773 2,620,554 12/ 1952 Mochel et al.29-1568 3,053,694 9/1962 Daunt et al 29-1568 X a LAVERNE D. GEIGER,Primary Examiner.

BRADFORD KILE, Assistant Examiner.

